POST-CRETACEOUS HISTORY OF WESTERN WYOMING 323 



glaciation; but, after having studied the deposits of more than 

 forty-five Pleistocene glaciers, distributed over a large part of west- 

 ern Wyoming, I find it no easy task to reduce the facts to such 

 comfortable simplicity. Indeed, if disposed to support arbi- 

 trarily the hypothesis that there have been many successive 

 advances of glaciers, I could, by selecting cases, arrange a graded 

 series leading by almost imperceptible steps from the least modified 

 glacial deposits which have been practically unaffected by post- 

 glacial changes, to those which have lost most of their glacial char- 

 acteristics and have been eroded to isolated remnants. Before 

 discussion of the question of successive glacial stages some general 

 considerations need attention. 



The glacial features in the several valleys differ from each other 

 in many respects, among which the following are important: 

 {a) the depth to which moraines have been intrenched by streams, 

 and the extent to which they have been reduced in area; (b) the 

 degree of preservation of distinctive glacial topography; (c) the 

 closeness of relation of the moraines to modern valleys and their 

 terraces; (d) the progress of weathering of glaciated rock surfaces 

 and of the bowlders upon the moraines; {e) the depth of soil, 

 particularly of loess, on the moraines. 



These attributes are influenced by more or less variable condi- 

 tions and one should be prepared to find drift deposits of essentially 

 the same age, changed much in some cases and little in others. 

 Lateral moraines resting upon soft clays may be rapidly destroyed 

 through the growth of gullies, while moraines planted firmly on the 

 hard Paleozoic or pre-Cambrian rocks suffer only trivial erosion 

 in the same length of time. Drift plastered along steep slopes may 

 be largely denuded while contemporaneous moraines lying upon 

 interstream plateaus retain their original topography. Ponds 

 without inlets apparently are filled much more slowly than those 

 entered by streams, especially if those streams are eroding soft 

 materials. Where the cKmate is dry, as in the Wind River 

 basin, it is probable that the bowlders on the moraines would 

 show fewer signs of decay than those in the moist forests on 

 the west slope of the Teton Mountains, and also that soil 

 and loess would accumulate more rapidly in the latter region, 



